Traffic separation problem at den causes an air carrier crew to slow below the ATC assigned speed.

Attributes
ACN	556253
Time
Date	200208
Day	Fri
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : den.airport
State Reference	CO
Altitude	msl single value : 8000
Environment
Light	Night
Aircraft 1
Controlling Facilities	tracon : d01.tracon tower : den.tower
Operator	common carrier : air carrier
Make Model Name	A310
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : rwy 16 other
Flight Phase	descent : approach
Route In Use	approach : visual
Flight Plan	IFR
Aircraft 2
Controlling Facilities	tower : den.tower
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	descent : approach
Route In Use	approach : visual
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	556253
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Events
Anomaly	conflict : airborne less severe non adherence : clearance non adherence : required legal separation other anomaly
Independent Detector	other controllera other flight crewa
Resolutory Action	none taken : anomaly accepted
Consequence	faa : reviewed incident with flight crew other
Supplementary
Problem Areas	ATC Human Performance Flight Crew Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Inter Facility Coordination Failure

Narrative:

We were unable to comply with ATC speed clearance. On vectors to intercept runway 16 localizer, den approach slowed us to 170 KTS and asked if we had the field in sight. We reported it in sight, so they cleared us for a visual approach to runway 16, maintain 190 KTS. As we speed back up to 190 KTS, we saw traffic who we thought was for runway 17R. The traffic then did a huge s-turn back to runway 16. We thought we were way too close (the traffic was never called to us), with TCASII range 3 mi and closing fast, so we advised approach that we were slowing for the traffic in front of us. Den approach asked us to maintain 170 KTS to leets and contact tower. There was convective WX in the area and a possibility of LLWS (though none had been reported yet). As we slowed to 170 KTS, distance was still closing and we could see that it was an air carrier Y aircraft. We contacted tower and advised them we were slowing for traffic in front of us (we were 3 mi from leets, and 170 KTS would bring us too close to aircraft in front of us. Tower responded with 'maintain 170 KTS to leets as previously instructed.' since we were only 1 mi from leets at 150 KTS (3 mi from traffic) we responded 'unable' and continued. We had advised them in plenty of time to slow aircraft behind us to correct their sequencing mistake.

Original NASA ASRS Text

Title: TFC SEPARATION PROB AT DEN CAUSES AN ACR CREW TO SLOW BELOW THE ATC ASSIGNED SPD.

Narrative: WE WERE UNABLE TO COMPLY WITH ATC SPD CLRNC. ON VECTORS TO INTERCEPT RWY 16 LOC, DEN APCH SLOWED US TO 170 KTS AND ASKED IF WE HAD THE FIELD IN SIGHT. WE RPTED IT IN SIGHT, SO THEY CLRED US FOR A VISUAL APCH TO RWY 16, MAINTAIN 190 KTS. AS WE SPD BACK UP TO 190 KTS, WE SAW TFC WHO WE THOUGHT WAS FOR RWY 17R. THE TFC THEN DID A HUGE S-TURN BACK TO RWY 16. WE THOUGHT WE WERE WAY TOO CLOSE (THE TFC WAS NEVER CALLED TO US), WITH TCASII RANGE 3 MI AND CLOSING FAST, SO WE ADVISED APCH THAT WE WERE SLOWING FOR THE TFC IN FRONT OF US. DEN APCH ASKED US TO MAINTAIN 170 KTS TO LEETS AND CONTACT TWR. THERE WAS CONVECTIVE WX IN THE AREA AND A POSSIBILITY OF LLWS (THOUGH NONE HAD BEEN RPTED YET). AS WE SLOWED TO 170 KTS, DISTANCE WAS STILL CLOSING AND WE COULD SEE THAT IT WAS AN ACR Y ACFT. WE CONTACTED TWR AND ADVISED THEM WE WERE SLOWING FOR TFC IN FRONT OF US (WE WERE 3 MI FROM LEETS, AND 170 KTS WOULD BRING US TOO CLOSE TO ACFT IN FRONT OF US. TWR RESPONDED WITH 'MAINTAIN 170 KTS TO LEETS AS PREVIOUSLY INSTRUCTED.' SINCE WE WERE ONLY 1 MI FROM LEETS AT 150 KTS (3 MI FROM TFC) WE RESPONDED 'UNABLE' AND CONTINUED. WE HAD ADVISED THEM IN PLENTY OF TIME TO SLOW ACFT BEHIND US TO CORRECT THEIR SEQUENCING MISTAKE.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.